1. Field of the Invention
The present invention relates to a phase-change optical information recording medium in which information may be recorded and reproduced by irradiating a beam to a recording layer to generate optical change of material of the recording layer, thereby simultaneously rewriting the information, and an optical information recording and reproducing apparatus and method for the same.
2. Description of the Related Art
In conventional optical information recording and reproducing apparatuses using phase-change optical information recording media, a wavelength-dependent filter has been used to obtain a beam having a wavelength suitable for recording and reproducing operation. Exmaples of the wavelength-dependent filter include quarter wavelength plate and a filter using liquid crystals to change a numerical aperture.
Japanese Patent Application Laid-Open (JP-A) No. 05-234136 discloses a better technique to reproduce optical information than optical resolution, introducing a filter made of an optical material having two or more of either non-linear transmittance or reflective properties, increasing a diameter of the recording beam, and decreasing a diameter of the reproducing beam at the same time.
Phase-change optical information recording media are used as a rewriting media for CD (CD-RW) or DVD. In the conventional phase-change optical information recording medium, a red LD (recording wavelength 600 to 830 nm) was used to conduct recording and reproducing operations. Recently, use of a blue LD (recording wavelength 390 to 430 nm) has been proposed in order to increase the recording capacity. However, when conducting recording and reproducing operations on a phase-change optical information recording medium with a blue LD, the noise level is high in the low power region, and it particularly becomes evident during reproducing operation.